1. Field of the Invention
The present invention relates to a head-protecting air bag apparatus which is adapted to eject a gas from an inflator when a predetermined heavy load is applied to a side of a vehicle body, so as to inflate by means of the gas an air bag stored in such a manner as to extend from a pillar section along a roof side rail.
2. Description of the Related Art
Conventionally, head-protecting air bag apparatuses have already been proposed in which, in order to improve performance of protecting the head of a vehicle occupant seated in a front seat when a predetermined heavy load is applied to a side of a vehicle body, an air bag folded and stored in such a manner as to extend from a front pillar section along a roof side rail is inflated along a side window glass. Hereafter, a description will be given of the arrangement shown in WO 96/26087 which discloses this type of head-protecting air bag apparatus.
As shown in FIG. 7, a head-protecting air bag apparatus 100 has as main components thereof: an elongated duct 106 disposed in such a manner as to extend from a front pillar section 102 along a roof side rail 104; an air bag 112 which is folded and stored in the duct 106 and fixed to a vehicle body at a front end fixing point 108 and a rear end fixing point 110; an inflator 116 which is connected to a rear end of the duct 106 through a hose 114 and is adapted to eject a gas when a predetermined heavy load is applied to the side of the vehicle body; and a belt-shaped strap 118 having one end fixed to the vehicle body and the other end fixed to a rear end portion of the air bag 112. Further, the air bag 112 is formed by connecting a plurality of cells 120 which are respectively formed in a substantially cylindrical shape and arranged such that longitudinal directions thereof are substantially parallel to the vertical direction of the vehicle.
In the above-described structure, when a predetermined heavy load is applied to the side of the vehicle body, the gas is ejected from the inflator 116. For this reason, the ejected gas flows into the cells 120 of the folded air bag 112 through the hose 114 and the duct 106. Consequently, the cells 120 are inflated to the substantially cylindrical shape and arranged such that the longitudinal directions thereof are substantially parallel to the vertical direction of the vehicle, and thereby the air bag 112 is expanded and suspended like a curtain along a window glass 122. Further, since the rear end portion of the air bag 112 is connected to the vehicle body by the strap 118, the rear side of the air bag 112 is surely disposed on an inner side of an upper portion of a center pillar section 124.
However, in the above-described head-protecting air bag apparatus, high gas pressure acts on a portion of the air bag 112 close to the inflator 116 due to the flowing gas from the inflator 116. For this reason, as shown in FIG. 8, in a case where an inflator 130 is provided on a front pillar section 132, and where a pillar guide portion 136 of an air bag 134 formed along the front pillar section 132 is contracted into a tubular shape by means of a joined portion 138 formed by sewing, bonding, or the like, a flow of the gas (arrow W in FIG. 8) during the early period of the expansion of the air bag changes suddenly in a vicinity of a rear end 136A of the guide portion 136, which forms an outlet of a tubular portion. In addition, since an upper fastened portion of an unillustrated front pillar garnish is located in a vicinity of the rear end 136A of the guide portion 136, the load applied to the upper fastened portion of the front pillar garnish increases due to the aforementioned change in gas pressure. Accordingly, in the head-protecting air bag apparatus such as the one shown in FIG. 8, it is necessary to reinforce the upper fastened portion of the front pillar garnish, and the like.
Moreover, in the head-protecting air bag apparatus such as the one shown in FIG. 8, during the early period of inflation of the air bag 134, the load increases at noninflatable portions 140, 142 and 144 located downstream of the rear end 136A of the pillar guide portion 136, particularly at the noninflatable portion 140 located in the vicinity of the rear end 136A of the guide portion 136.